1. Field
The presently disclosed subject matter relates to an LED optical unit using an LED light source and a projector lens and vehicle headlights including the LED optical unit, and more particularly to the vehicle headlights including the LED optical unit having a high cooling efficiency even when the LED light source is located extremely close to a light incoming surface of the projector lens.
2. Description of the Related Art
Recently, various vehicle headlights using an LED light source have been developed. This development has been brought about because the LED light source has a long life and is battery friendly as compared with a light bulb, discharge lamp, etc. On the other hand, because the LED light source may generate a large amount of heat when the LED light source having a favorable light distribution is provided for the vehicle headlights, various cooling structures for the LED light source have been developed.
A conventional headlight shown in FIG. 14 is a projector headlight that is disclosed in patent document No. 1 (Japanese Patent Application Laid Open JP2009-21135). The projector headlight includes: an LED light source 34 mounted on a base substrate: a reflector 35 for reflecting light emitted from the LED light source 34: a projector lens 37 for emitting the light reflected by the reflector 35 with a predetermined light distribution pattern; a shade 36 for forming a cutoff line; a heat sink 39 to radiate a heat generated from the LED light source 34; a heat pipe 38 that transmits the heat of the LED light source 34 from the base substrate to the heat sink 39; a housing 31 for fixing the heat sink 39; a lens holder 33 that attaches the projector lens 37 and the shade 36 to the housing 31; and an outer lens 32.
In the above-described projector headlight, the heat developed by the LED light source 34 is transmitted from the base substrate to the heat sink 39 via the heat pipe 38 and is radiated from the heat sink 39. Accordingly, an increase of a junction temperature of an LED chip that is included in the LED light source 34 can be prevented.
In addition, when the projector headlight is provided with the reflector 35 that is composed of an ellipsoidal surface, the LED light source 34 may be located at a first focus of the reflector 35 and a second focus of the reflector 35 may be located at a focus of the projector lens 37. Therefore, because a distance between a light incoming surface of the projector lens 37 and the LED light source 34 may become relatively long, the projector lens 37 may be hardly influenced by the heat generated from the LED light source 34.
However, it is difficult to shorten a thickness between the projector lens 37 and the heat sink 39, although it is easy for the projector headlight to form a favorable light distribution pattern. Therefore, the conventional projector headlight may be difficult to package in a small size car. In order to reduce the thickness of the projector headlight, another conventional projector headlight shown in FIG. 15 is disclosed in patent document No. 2 (Japanese Patent Application Laid Open JP2009-146665).
The other conventional projector headlight includes: a lens holder 43 formed in a substantially hemispherical shape; an LED light source 44 mounted on a base substrate 48 that is attached on an inner surface of the lens holder 43; and a projector lens 47 attached to the lens holder 43 so that a light incoming surface thereof faces the LED light source 44. Accordingly, because the conventional projector headlight is not provided with a reflector unlike the projector headlight shown in FIG. 14, the thickness of the projector headlight may become thinner than that of the conventional projector headlight of FIG. 14.
However, the light incoming surface of the projector lens 43 is located extremely close to the LED light source 44, and therefore may be easily influenced by a heat generated from the LED light source 44. Consequently, the projector headlight is provided with a cutout section 43A over the LED light source 44 in the lens holder 43 as shown in FIG. 15. The heat generated from the LED light source 44 may be radiated from the cutout section 43A of the lens holder 43. Therefore, an increase of a junction temperature of an LED chip that is included in the LED light source 44 may be prevented.
However, in the conventional projector headlight shown in FIG. 15, although the cutout section 43A is provided over the LED light source 44 in the lens holder 43, the cutout section 43A may not be provided under the light source 44. Accordingly, the conventional projector headlight may not create an air flow between the light incoming surface of the projector lens 47 and the LED light source 44 so that the heat generated from the LED light source 44 can be efficiently radiated. Thus, the increase of the junction temperature of the LED chip that is included in the LED light source 44 may not be efficiently prevented.
The above-referenced Patent Documents are listed below and are hereby incorporated with their English abstracts in their entireties.    1. Patent document No. 1: Japanese Patent Application Laid Open JP2009-21135    2. Patent document No. 2: Japanese Patent Application Laid Open JP2009-146665
The disclosed subject matter has been devised to consider the above and other problems, characteristics and features. Thus, an embodiment of the disclosed subject matter can include a vehicle headlight including a small projector type LED optical unit that can radiate a heat generated from an LED light source with a high cooling efficiency and can be easily assembled with a simple structure. In this case, the vehicle headlight can be constructed from a single projector type optical unit that can be formed in a thin shape. Thus, the vehicle headlight can result in an increase in the possible range of headlight design, and therefore can be employed for various vehicles including a small size car.